1. Field of the Invention
The present invention relates to an information storage device and method for reducing airborne noise and vibration. Particularly, the present invention relates to an airflow damper that reduces airborne noise and vibration in hard disk drive devices.
2. Description of the Related Art
Airflow within a hard disk drive assembly generally tends to vibrate the disks during rotation, generating undesired noise in the hard disk drive assembly. In order to understand why airflow has such an important role in regulating airborne noise, it is necessary to examine airflow characteristics in a hard disk assembly (HDA).
FIG. 1 illustrates the main airflow streams in a conventional hard disk assembly.
As shown in FIG. 1, the hard disk assembly (HDA) 100 includes a hub 110, first and second disks 120 and 130 mounted on hub 110, and a housing cover 140. The first and second disks 120 and 130 are rotated by hub 110. In FIG. 1, h is understood to be the distance between upper disk 120 and the top inner surface of housing cover 140, and dxcex8dxcex8is understood to be the distance between the edges of disks 120, 130 and the sidewall of housing cover 140.
When first and second disks 120 and 130 are rotatably driven by hub 110, the disks pull fluid (air) axially downward and pump the air radially outward. For example, air is pulled downward along hub 110 from the space above rotating disk 120. This axial downward air then flows radially outward along the upper surface of rotating disk 120.
The main airflow in HDA 100 is thus tangential to the circumferential edge of rotating disks 120 and 130, as represented by the upward and downward arrows along the periphery of rotating disks 120 and 130. The radially outward flow along the surface of the disks operates as a secondary flow caused by a rotating boundary layer. The rotating boundary layer that is formed is designated by xcex4m and xcex4f in FIG. 1, and is commonly referred to as the Ekman layer, which will be described in greater detail as follows.
A qualitative description of airflow and the boundary layers is as follows. Because of the no-slip condition of disks 120 and 130 with respect to airflow, fluid in contact with the surface of the rotating disks 120 and 130 rotates with the same angular velocity as the disk surface, and experiences the same centripetal acceleration. At the start of motion of the disks, a boundary layer of fluid begins to form in the circumferential direction. The fluid in the boundary layer begins to spin, but cannot maintain the same centripetal acceleration as the surface of the disk, because of fluid viscosity. Because of this, the boundary layer acquires an outward radial component. As the radial component of fluid flow increases in magnitude, a secondary fluid layer develops in a radial direction, having stresses that are centrally directed. These stresses provide the secondary fluid layer with a central force, and have a centripetal acceleration that is greater than zero but less than that of the surface of the disk. This secondary fluid layer, which may be understood as having components xcex4m and xcex4f as designated in FIG. 1, comprises the Ekman layer.
The Ekman layer component xcex4m is formed near the surface of the disk 120 by disk rotation, and is defined as having a thickness (depth in the vertical direction) of 4xcex4, whereby:                               δ          ~                                    v              Ω                                      ,                            Eq        .                  xe2x80x83                ⁢                  (          1          )                    
and wherein v is the dynamic viscosity of the fluid forming the boundary layer and xcexa9 is the angular velocity of the disk. The Ekman layer component xcex4f is formed near the top inner surface of housing cover 140 by fluid (air) rotation, and is defined as having a thickness (or depth in the vertical direction) of 8xcex4.
By way of example, if xcexa9=5,400 rpm, xcex4=0.17 mm (the dynamic viscosity of air is 1.59xc3x9710xe2x88x925/m2/s). The Ekman layer component xcex4m thus has a thickness of 0.68 mm and the Ekman layer component xcex4f has a thickness of 1.36 mm. Likewise, if xcexa9=7,200 rpm, xcex4=0.15 mm, the Ekman layer component xcex4m has a thickness of 0.60 mm and the Ekman layer component xcex4f has a thickness of 1.2 mm.
As further illustrated in FIG. 1, a large vortex 102 is created between secondary fluid layers xcex4m and xcex4f which comprise the Ekman layer. The creation of large vortex 102 excites disk fluttering during operation of the HDA, thus increasing noise level.
The present invention is therefore directed to an information storage device and method for reducing airborne noise and vibration, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
Accordingly, to solve the above and other problems, it is an object of the present invention to provide a hard disk drive and method for reducing airborne noise and vibration, that prevents formation of a large air vortex above the disks in the hard disk assembly during rotation of the disks.
The above and other objects may be achieved by a hard disk assembly including in combination a housing; a hub within the housing; at least one disk mounted on the hub and rotated by the hub; and an airflow damper, mounted on an upper surface of an interior of the housing, that prevents formation of a vortex above the at least one disk during rotation of the at least one disk, the airflow damper having a thickness related to rotational speed of the at least one disk.
The above and other objects may also be achieved by a method of preventing vortex formation in a hard disk assembly, the hard disk assembly having a housing with a hub therein on which at least one disk is mounted and driven to be rotated, the method including providing an airflow damper on an upper surface of an interior of the housing, the airflow damper having a thickness related to rotational speed of the disk.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.